The heating system of a motor vehicle generally comprises a heat exchanger through which the engine coolant is circulated, including fan means for circulating the air of the passenger compartment through the heat exchanger. Such systems only operate when the engine is running since the coolant is circulated by mechanical pumps operating directly off the engine. It has long been known that it would be desirable to be able to continue heating the passenger compartment without running the engine. For example, U.S. Pat. Nos. 2,170,032 issued to Page, 2,230,051 issued to Conklin, 2,801,802 issued to Jackson, and British Pat. No. 1,551,296 issued to Arden-Mark, Inc. all disclosed auxiliary circulation devices for effecting circulation of engine coolant through a vehicle heater system after engine shutdown. The devices disclosed in these patents all disclose the use of an auxiliary pump driven by an electric motor inserted into the engine coolant circulation system which may be actuated upon engine shutdown to thereby continue the circulation of engine coolant through the heater of the vehicle.
In the Page and Conklin devices, a simple on/off switch is employed to actuate the auxiliary pump. The Jackson and Arden-Mark devices additionally employ a thermostatic switch for automatically shutting off the auxiliary pump and fan motor when the temperature of the coolant drops below a predetermined level.
It is an object of the present invention to provide an improved auxiliary circulation system for vehicle heaters having a voltage monitor which permits the system to operate only when the power supply of the vehicle falls within predetermined limits.